1. Field of the Invention
The present invention relates to a method of forming a carbon nanotube structure and a method of manufacturing a field emission device using the method of forming a carbon nanotube structure, and more particularly, the present invention relates to a method of forming a high quality carbon nanotube structure at a low temperature and a method of manufacturing a field emission device using the method of forming a carbon nanotube structure.
2. Description of the Related Art
A Field Emission Device (FED) emits visible light due to the collision of electrons emitted from emitters formed on a cathode electrode with a phosphor layer formed on an anode electrode. The FED can be applied to a FED back light unit of FEDs that form images using field emissions or a field emission backlight unit of Liquid Crystal Displays (LCDs).
In the FED, a micro tip formed of a metal, such as Mo, is used as a conventional emitter of electrons. However, recently, carbon nanotubes (CNTs) have been mainly used as emitters. FEDs that use CNTs as emitters have a high possibility of being applied to various fields such as a car navigation apparatus or a view finder for electronic image displays due to a wide viewing angle, high resolution, low power consumption, and temperature stability of the FEDs. In particular, the FEDs that use CNTs as emitters can replace a display apparatus in personal computers, Personal Data Assistants (PDAs), medical instruments, or High Definition TeleVisions (HDTVs).
In manufacturing FEDs using CNTs, the obstacles that are faced are an increase in lifetime, manufacturing a large screen, reducing costs, and reducing an operating voltage.
In order to increase the lifetime of the FED, CNTs can be synthesized using a Chemical Vapor Deposition (CVD) method. In this method, the degradation of the CNTs can be prevented by growing the CNTs directly on a substrate without using an organic binder, thus increasing the lifetime of the FED. But, this method has drawbacks in that an adhesion force between the CNTs and the substrate is weak since an organic binder is not used and the activity of a catalyst layer for growing the CNTs is reduced since the catalyst layer reacts with the substrate.
The manufacture of a large screen and reduction in cost of the FEDs can be achieved by using an inexpensive sodalime glass substrate. However, the sodalime glass substrate has a relatively low deformation temperature of approximately 480° C. In other words, the synthesis of the CNTs on the sodalime substrate using a CVD method must be performed at a temperature lower than 480° C. However, it is technically very difficult to do so. That is, in order to synthesize the CNTs at a low temperature, reaction gases must decompose at a temperature lower than 480° C., and must meet a complicated reaction condition whereby the decomposed gases must be precipitated by diffusing into a catalyst layer.
In order to reduce an operating voltage of the FEDs, it is necessary to control the density of the synthesized CNTs. One of the reasons why the CNTs are used as emitters in the FEDs is that the CNTs have a high field enhancement effect due to a large aspect ratio of each of the CNTs. However, if the density of the CNTs is too high, the aspect ratio of a CNT bundle is much less than each of the CNTs. In such a case, a high operating voltage is required in order to emit electrons. To solve this problem, the density control of the CNTs is important.
During a synthesizing process of the CNTs, a catalyst layer must be present as particles so that carbon atoms that are diffused into the catalyst layer can be precipitated in a tube shape. However, the catalyst layer has a tendency of agglomerating at a synthesizing temperature of the CNTs. Therefore, there is a need to prevent the catalyst layer from agglomerating during the synthesizing process.